Method of manufacturing electron-emitting cathodes



Patented July 10, 1928.

UNITED STATES.

PATENT OFFICE.

GUSTAV LIEBERT, OF NUREMBERG, GERMANY, ASSIGNOR T0 SUDDEUTSCHEN TELE- PHON-APPARATE-, KA BEL- U. DRAHTWERKE AK'I'IEN' GESELLSCHAFT, OF NUREM- BERG, GERMANY.

METHOD OF MANUFACTURING ELECTRON-EMITTING CATHODES.

No Drawing. Application'iiled July 1, 1925, Serial No. 40,956, and in Germany 'J'uly 24, 1924.

It is known that certain substances. more particularly the oxides of earth alkalies, emit electrons at a much lower temperature than the metals which melt at a higher temperature. For this reason the said substances are employed for the manufacture of cathodes for electric discharge vessels of any kind. The supports of the substances emitting the electrons consist of wires or metal bands which are often twisted in order to increase their strength, the electron emit-- ting substances being coated thereon. There are various methods of coating the electron emitting substances, amongst them, the following one. The electron emitting substances are mixed in a definite proportion with hydro-carbon of high molecular weight, for instance, paraffin or colophony and the mixture thus obtained is coated on the support, consisting for instance of a platinum, or a platinum-iridium filament. Use is made either of the oxides themselves, or of a compound which passes into oxide in the presence of oxygen, at a definite temperature.

It has been found that this known method requires a refinement, in order to produce oxide coated cathode tubes, which are really uniform, as is nowadays absolutely necessary in the art of thermionic tubes.

emit electrons uniformly at all the points,

I for which reason, for instance, in the case sufliciently fine, which result cannot be attained with the usual method of manufac ture of the oxide coated cathodes. The or- V ganic means with which the oxide is mixed.

1s rendered fluid by heating and the electron emitting substance is placed therein in the form .of powder. It will thus easil be seen that in this case, as in the case 0 any A fault that often occurs is that the cathode does not obtain a high uniformity and great smoothness of the cathodes.

The method according to the present invention is carried out as follows The resin is powdered until it is reduced to fine dust, which in order to obtain a further fineness is passed through a hair sieve. The compound which is used for the emission is treated in exactly the same way. Thereupon the two substances are intimately mixed with one another until a very homogeneous. powder is obtained. By grinding the two substances together in a mortar, the,

mixture can be made more intimate than by simply stirring thesubstanc'es together. The powder thus obtained is then slowly heated. The melting of the hydro-carbon causes a yery homogeneous mixture between the resin and the oxide to be obtained whilst the formation of lumps is completely avoided.

The sieve used for sifting is preferably of such a mesh, that only those particles which have a diameter smaller than 1/20v mm. can pass through. In order further to improve the result it is desired to attain,

the oxide is allowed to settle down, under very slow cooling, and only the uppermost portion is employed for coating the cathode.

at I claim is 1. A method of manufacturing electron emitting cathodes consisting in first intimately mixing .an electron emitting substance with a carbon compound of high molecular weight, both in a finely pulverized form, then heating and fusing them together, and finally coating the cathode with the substance thus produced.

2. A method of manufacturin according to claim 1, and in whie the electron emitting substance. and the carbon compound are passed through a sieve before they cathodes are'fused together, so that only particles 1 smaller than 0.05 mm. diameter are emthe upper portion thereof being used for the ployed. coating of the cathode. 3. A method of manufacturing cathodes In testimony whereof I hereunto aflix my 10 according to claim 1, and in which after signature. 5 the electron emitting substance'and the oarv bon compound have been fused together, the mass thus" obtained is cooled slowly, only GUSTAV LIEBERT. 

